This invention relates to a device as defined in claim 1, said device being intended for use particularly in the reinforcement of teeth or dental prosthetic devices.
Fiber products are generally used in dentistry for splinting and reinforcing of teeth and for reinforcing of various dental prosthetic devices such as crowns, fixed bridges, removable dentures and so called surface attachable bridges or light or maryland type bridges. Such fiber reinforcement products either solely consist of fibers, or they are fiber reinforcement products preimpregnated with a polymer or a monomer. Commercially available products of this kind are listed in the following table 1.
TABLE 1 ______________________________________ Type of fiber Product (brand) Preimpregnation ______________________________________ UHMWP.sup.x) Ribbond, DVA Fibers none Connect, Fibre-Bind Fibrespan monomer Aramide Kevlar none Glass GlassSpan, Fiber Splint none Vectris, FibreKor monomer Stick, Stick Net polymer ______________________________________ .sup.x) UHMWP = ultra high molecular weight polyethylene
In the UHMWP products, there is no attachment between the fibers and the polymer, the impregnation of the fibers is poor and the products result in an increase of fatigue strength of only about 25%.
In aramide fiber products the fibers do not either attach very well to the polymer and the impregnation of the fibers is poor.
In glass fiber products without preimpregnation by a polymer matrix, the impregnation of the fibers is poor and their strengths are poor.
The preimpregnated glass fiber products are expensive, but they result in a good strength. The international patent publication WO 96/25911 discloses such a porous prepreg based on glass fibers, wherein said prepreg is preimpregnated with a polymer.
The commercially available fiber reinforcement products are usually in woven form or in the form of a fiber bundle where the fibers are unidirectional. The handling of woven fiber products is rather easy. When such products are cut e.g. with scissors, the fiber bundles are fairly well kept together and they do not fray remarkably. The handling of non woven fiber bundles of unidirectional fibers is remarkably more difficult. When these products are cut, the individual fibers are not kept together by anything, and the fiber bundle may freely fall apart. This problem has been attempted to solve by tying the bundle together with an additional thread, by weaving the bundle or by preimpregnating the bundle with a porous polymer matrix. These solutions imply new problems. If the bundle is tied together with a thread or is woven, the fibers stay tightly together. This complicates the impregnation of the fiber bundle because the monomer liquid cannot easily penetrate in between the individual fibers. Another problem is that if the bundle is tightly tied or woven together, the fibers of the fiber bundle cannot be spread any longer. Fiber bundles impregnated with a polymer are easy to cut and they impregnate well with the monomer because of the existing polymer matrix between the fibers. Once impregnated with the monomer, the polymer matrix begins to dissolve into the monomer and the individual fibers begin to loosen from the bundle. As a result, the fiber bundle is difficult to handle on the mould or in the mouth because the fiber bundle is no longer well bound together. Secondly, a problem common to all types of glass fiber bundles is that the high tensile modulus of glass fibers forces the bundle to straigthen up. Therefore it is very difficult to apply the bundle onto curvy tooth arches.
In summary, the aim is that the fibers either can be kept together or spread, if desired. Furthermore, it is desirable that the fiber bundle can be formed to follow the shape of the tooth arch closely while keeping the control of the fibre bundle continuously. In addition, it is desirable that the wetting of the fiber bundle and the handling and storage thereof is safe because of the repeated skin contamination and the allergenic properties of the evaporating monomer. Moreover, it is desirable that the wetted fiber bundle, which at a later stage is cured with light (blue light), is not cured by room light or by the curing light from the light curing apparatus before the wetted fiber bundle is applied on the intended place.